Polymers fluorescence

Poly[2,5-dialkoxy-l,4-phenylene) vinylenejs with long solubilizing alkoxy chains dissolve in conventional organic solvents such as chloroform, toluene, or tetrahydrofuran [21, 28, 32-36]. Their emission and absorption spectra are red-shifted relative to PPV itself, and the polymers fluorescence and electroluminescence quantum yields are greater than parent PPV. This benefit may be a consequence of the long alkyl chains isolating the polymer chains from each other. 

For this purpose, stabilization efficiency was defined as 1-As/Aq, where As and Aq represent the increase in absorbance in the blue spectral region (yellowing) in the presence and absence of stabilizer, respectively. The resulting stabilization efficiencies were found to decrease substantially over relatively short exposure times (ca. 40% decrease between 10 and 25 hrs irradiation). Difference absorption spectra obtained during accelerometer exposure exhibited a new absorption band at ca. 300 nm which overlapped strongly with polymer fluorescence (required for efficient RET quenching) and weakly with polymer absorption (screening).1... 

There is no reason why the same principle cannot be applied for light-emitting polymers as host materials to pave a way to high-efficiency solution-processible LEDs. In fact, polymer-based electrophosphorescent LEDs (PPLEDs) based on polymer fluorescent hosts and lanthanide organic complexes have been reported only a year after the phosphorescent OLED was reported [8]. In spite of a relatively limited research activity in PPLEDs, as compared with phosphorescent OLEDs, it is hoped that 100% internal quantum efficiency can also be achieved for polymer LEDs. In this chapter, we will give a brief description of the photophysics beyond the operation of electrophosphorescent devices, followed by the examples of the materials, devices, and processes, experimentally studied in the field till the beginning of 2005. 

Keywords Conjugated polymer Fluorescent sensor FRET Turn-off Tum-on... 

The application of vb-DMASP to MIPs was continued in subsequent works [64, 65], In these investigations, time-resolved fluorescence spectroscopy was applied to study bulk fluorescent MIP. The imprinted polymer fluorescence quenching with increasing concentrations of aqueous cAMP was determined from the fluorescence lifetime parameters. Two components in the fluorescence decays were identified and assigned to two different types of cavities present in the polymer matrix. One was accessible and open to binding, whereas the other was inaccessible, being buried inside the bulk polymer. The fluorescence lifetime decreased due to the increase in the concentration of the initial target analyte. However, the accessible... 

The Ksv values for these ions are similar to those for Cu2+ and it may be anticipated that binding to the polymer by all three ions occurs with comparable strength due to reasonably similar Coulombic interactions between the divalent ions and the polymer. Since the polymer fluorescence is known to be strongly attenuated when interchain or intermolecular interactions occur, it may be that all or part of the quenching observed for these ions may be attributed to aggregation effects induced by association of the divalent cations with the polymer. 

Figure 2 Two-stage use of the QTL approach for competitive assay and/or drug discovery. In the upper part the polymer QTL complex (nonfluorescent) is treated with a bioagent-receptor and formation of the bioagent QTL complex results in freeing the polymer of the quencher and turning on the polymer fluorescence. If a mixture of polymer and bioagent QTL complex (fluorescent) is exposed to a new molecule capable of binding with the bioagent, release of the QTL from the complex leads to its association with the polymer and a turning off of the polymer fluorescence.

Figure 5.27 Schematic representation of the polymeric Jelley or Scheihe assemblies of isocyanine dyes. An imine carbon atom acts as electron acceptor (a), an enamine nitrogen as donor (d). If the angle a is much below 54°, long wavelength polymer bands are observed. The rigid polymer fluoresces.

Keywords Cyclosilanes / Siloxene / Polymers / Fluorescence Spectra... 

The substitution in polymer-fluorescent dye-competitor systems has been investigated by fluorescence analysis and depending on their ability to substitute dyes competitors... 

The fluorescence of the phenyl polymer is similar in shape to the fluorescence from the alkyl polymers and the similar shape of the phosphorescence spectrum, as well, suggests that the origins of the electronic spectrum are also much the same. The apparent increased quantum yield for phosphorescence in poly(phenyl methyl silylene) probably reflects a mixing of the ring electronic levels with the levels of the chain. Both the fluorescence and phosphorescence of the naphthyl derivative are substantially altered relative to the phenyl polymer. Fluorescence resembles that of poly(B Vinyl naphthalene) (17,29) which is attributed to excimer emission. Phosphorescence is similar to naphthalene itself. These observations suggest that the replacement of an alkyl with phenyl moiety does not change the basic nature of the electronic state but may incorporate some ir character. Upon a naphthyl substitution both the fluorescence and phosphorescence become primarily tt-tt like. 

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